Final answer:
A speed reduction warning sign provides advance notice of an upcoming speed limit change, which is distinct from the actual speed limit sign.
Step-by-step explanation:
A warning sign of a speed reduction commonly serves as an indicator to drives about an upcoming change in the speed limit. This type of sign provides advance notice to drivers about a reduction in the speed limit ahead, allowing for a safe transition to the lower speed. It's important to differentiate between a speed reduction warning sign and the actual regulatory sign that states the speed limit at which drivers must not exceed.
The posted speed limit is the legally enforceable limit at which vehicles may travel in a specific area. Meanwhile, factors such as ideal speed, de jure, and de facto speed limits relate to the general practices and enforcement of traffic laws, which might influence how drivers decide to regulate their speed.